The present invention relates to air cushion type undercarriage devices such as are discussed and disclosed for example in my earlier U.S. Pat. Nos. Re. 26,812; 3,690,401 and 3,738,597; and more specifically relates to the problem of reducing the wear and tear rates of the apertured ground-tangent portions thereof. Previously, it has been proposed to alleviate the aforesaid problem by armoring the wear and tear recipient regions of the trunk fabrication such as with metal grommets or "overply" tread layers of similar material fabrications of substantial thicknesses and of compatible elasticity characteristics. However, such prior systems have been found to be inherently vulnerable to severe propagations of trunk fabric tear/cut stresses extending throughout the structures, especially within the relatively stiffer and thicker overply layers thereof. Such troubles as delamination, interply bond failure, and surface cut propagations develop to intolerable degrees, especially in the regions of the maximum strain areas of the trunk construction. In any case ground tangent surface wear is also a key factor in trunk life, especially whenever the vehicle is operative relative to concrete runways and the like.